Fused salt electrolyzer for magnesium production

ABSTRACT

An electrolyzer for the manufacture of magnesium, which has at least one electrolysis compartment with a cathode in the form of a frame whose members make up a closed loop around an anode in the electrolysis compartment.

United States Patent Strelets et al.

[151 3,676,323 [451 July 11, 1972 [54] F USED SALT ELECTROLYZER FORMAGNESIUM PRODUCTION [72] Inventors: Khaim Lipovich Strelets, ulitsaFurmanova, 19, kv. 2; Alexandr Sergeevich Chesnokov, ulitsaSchastlivaya, 9, kv, 28, both of Leningrad; Vladimir NikolaevichDevyatkin, prospekt Lenina, 43, kv. 9, Berezniki Permskoi Oblasti;Alexandr Nikolaevich Tatakin, ulitsa Gornyakov, l3, kv. 3, SolikamskPermskoi Oblasti; Evsei Dmitrievich Krasikov, Slavyansky bulvar, 3, kv.51, Moscow; Ljudmila Sergeevna Leonova, ulitsa Lornonosova, 105, kv.151; Galina Arkadievna Medvetskaya, ulitsa Lva Tolstogo, 68, kv. 53,both of Berezniki Permskoi Oblasti; Tatyana Georgievna Nechaeva, ulitsaMira, 42, kv. 73, Solikamsk Permskoi Oblasti, all of USSR [22] Filed:Dec. 10, 1970 [21] Appl. No.1 96,835

[52] US. Cl ..204/244, 204/70, 204/245, 204/ 272 [51] Int. Cl. ..C22d3/02, C22d 3/08 [58] Field of Search ..204/243-247, 70,

[56] References Cited UNITED STATES PATENTS 3,396,094 8/1968Sivilottietal ..204/70 3,580,835 5/1971 Peterson- ..204/70X FOREIGNPATENTS OR APPLICATIONS 238,791 12/1969 U.S.S.R ..204/243 R Primary Examinerlohn H. Mack Assistant-ExaminerD. R, Valentine Attorney-Holman &Stern [57] ABSTRACT An electrolyzer for the manufacture of magnesium,which has at least one electrolysis compartment with a cathode in theform of a frame whose members make up a closed loop around an anode inthe electrolysis compartment.

4 Claims, 3 Drawing Figures A 1T5 5\M FJl J J .T

H NH 7 SHEET 10F 3 P'A'TENTEnJuL 1 1 m2 III PATENTEDJUL 11 I972 3. 6 76323 SHEET 3 OF 3 FIG. 3

F USED SALT ELECTROLYZER FOR MAGNESIUM PRODUCTION The present inventionrelates to electrolyzers for the manufacture of magnesium.

Known in the art are electrolyzers for the manufacture of magnesium,comprising two compartments for the electrolysis of magnesium chloride,between which is placed a compartment to collect metallic magnesium.Between the electrolysis compartments and the collecting compartmentthere are par titions fabricated from refractory materials. Theelectrolysis compartments hold electrodes. Cathodes are provided in theform of plates with rods passing through a lining to a busbar.

However the above-mentioned electrolyzer has a low production rate.Attempts to increase the production rate of the electrolyzer byenlarging the electrolysis compartments reduce the current efficiencyand entail increased power consumption per unit of the quantity of metalproduced. Attempts to improve the production rate of the electrolyzer byincreasing its length results in requirement of extra shop floor areaand inconveniences in servicing. The multitude of cathodes, with eachcathode having a current-conducting connection of its own, passingthrough the lining, impair the strength of the lining at the fixationpoints. Another weak point about this type of electrolyzer lies in thatthe partitions made wholly of a refractory material. These partitionsfail at a high rate, resulting in loss of chlorine.

The main object of the present invention is to eliminate theabove-mentioned disadvantages. Other aims and advantages of theinvention will become more fully apparent from the followingdescription.

The object of the present invention is to provide an electrolyzer whichoffers a greater production rate, a high output of metal per unit area,improved utilization of the working volume, and simplified servicing,and has a reduced power consumption, fewer current-conductingconnections built into the lining and an extended service life.

This objective is accomplished by providing an electrolyzer for themanufacture of magnesium, which, according to the invention, has atleast one electrolysis compartment with a cathode in the form of a framewhose members form a closed loop around an anode in that compartment.

An electrolyzer of this type has a greater production rate.

It is expedient to make the members of the cathode (frame) in the formof walls and place the longitudinal walls between the electrolysiscompartment and the collecting compartment in such a way that theyconstitute the lower portion of a partition. With this construction, itis seen that the output of metal per unit area is increased.

It is further preferable that the thickness of the longitudinal membersof the cathode be made to increase towards the current-carryingconnection. This improves the operation of the electrolyzer and providesa more uniform distribution of current in the cross members of thecathode frame.

A greater production rate is obtained if the frame'shaped cathodes areinstalled in at least three electrolysis compartments with at least twocollecting compartments provided in between.

In a cell with three electrolysis the electrode in the middlecompartment may be about twice as wide as the electrode in the outerelectrolysis compartments. Thus better use is made of the operationalarea of an electrolyzer.

For a better understanding of the invention reference will now be madeto a preferred embodiment according to the invention and theaccompanying drawings, wherein:

FIG. 1 shows a cut-away view of an electrolyzer in plan, according tothe invention;

FIG. 2 shows vertical cross section lI-II through the electrolyzer ofFIG. 1;

FIG. 3 shows vertical longitudinal section III-III through theelectrolyzer of FIG. 1.

Referring to FIG. 1, the electrolyzer has two outer electrolysiscompartments 1 and one middle electrolysis compartment 1', between whichare placed compartments 2 (FIG. 2) for collection of metallic magnesiumand slime. The electrolysis compartments 1 and 1' hold graphite anodes 3and cathodes 4, said cathodes being in the form of a frame or a closedloop, each loop consisting of two longitudinal members 5 and severalcross members 6. The width of the longitudinal members 5 decreases inthe direction away from the current-conducting connection, which factprovides for a more uniform distribution of current in the cross members6 of the cathode frame.

For directed circulation of the electrolyte and better transfer of themetal (magnesium) from the electrolysis compartments into the collectingcompartments, the cross members 6 of the cathode frames (which are themain working surfaces of the cathodes) have bevelled portions 7 whichincrease the interelectrode distance in the direction of the collectingcompartments 2. The electrolysis compartments I and 1 are placed incommunication with the collecting compartments 2 by top and bottom slots8 (FIG. 3) in the partitions whose upper parts 9 (FIG. 2) are made of arefractory material. The lower portion of each partition is also one ofthe longitudinal members 5 of the cathode frame. The middle electrolysiscompartment l and the electrodes located in that compartment arerespectively twice as wide as the outer compartments 1 and theirelectrodes. The anodes are embedded in the brickwork of the electrolyzerbottom 10. Current to the anodes is conducted from beneath, through acast-iron contact slab 11 and an aluminum shank 12. The longitudinalmembers of the cathode frames extend through the elec-.

trolyzer lining 13 to a dc. source.

The electrolyzer operates as follows. The bath is filled with anelectrolyte consisting of molten chlorides of alkaline and alkalineearth metals to a level covering the slots 8 in the partitions. Thendirect current is applied to the electrodes, and the electrolysis of themagnesium chloride begins. The result is that magnesium and chloride areliberated at the respective electrodes. The operation is carried on atan electrolyte temperature of 680730 C. The electrolyte rises to thesurface and carries the magnesium and chlorine along; the chlorineleaves the electrolyte and collects at the top of the electrolysiscompartment. Chlorine removal from the electrolyzer is effected througha port in the top cover of the electrolyzer. The metal-electrode mixturefreed from chlorine flows from the electrolysis compartments through theslots 8 in the lower portion of the partition into the collectingcompartment. The magnesium metal collects at the top of the collectingcompartment, while the electrolyte flows through the lower portion ofthe partition back into the electrolysis compartment. In this way, thereis a closed flow of electrolyte providing for continuous transfer of themetal from the electrolysis compartments into the collectingcompartment. In the outer electrolysis compartments 1 the closed flow ofelectrolyte carries the metal in one direction, towards the collectingcompartment. In the middle electrolysis compartment, located between twocollecting compartments, a closed flow of electrolyte carries the metalin opposite directions, into the two collecting compartments. Therefore,the conditions for the transfer of the metal from the middleelectrolysis compartment which is nearly twice as long as the outer onesare the same as for the transfer from the outer compartments.

In the electrolysis compartment the spacing between the electrodesgradually increases in the direction of the collecting compartments.Therefore, the cell areas farthest from the collecting compartments havean increased current density and a maximum gas content in theelectrolyte, which factors provide for directed circulation of theelectrolyte essential to the transfer of the metal to the collectingcompartments across the entire width of the electrolysis compartments.

The metal is removed from the collecting compartments at regularintervals, as it collects there. The slirne from the electrolytesettling at the bottom is also removed periodically.

The electrolyzer described above has been tested. The energy consumptionhas been 12.5 kWh per kilogram of magnesium, which is 20 to 25 percentless than in the case of other existing electrolyzers In otherembodiments of the proposed electrolyzer, the 1ongitudinal members ofcathode frames may be of uniform crosssection along their entire length.Variations in the electrode spacing in the electrolysis compartment canbe obtained by using anodes with bevelled faces in the direction of thecollecting compartments. Also, current to the anodes may be suppliedfrom above.

What is claimed is:

1. An electrolyzer for the manufacture of magnesium, comprising incombination: at least three electrolysis compartments housingelectrodes; and at least one magnesium collecting compartment locatedbetween said electrolysis compartments each of the electrolysiscompartments having a plurality of anode members and a cathode in theform of a frame whose members form a closed loop around each anodemember in said electrolysis compartment.

2. An electrolyzer, as claimed in claim 1, which includes partitionwalls between electrolysis compartments and collecting compartments andin which said cathode members comprise longitudinal members which aremade in the form of walls which form a lower portion of the partitionwalls.

3. An electrolyzer, as claimed in claim 2, in which the thickness ofsaid longitudinal cathode members increases in the direction of thecurrent-conducting connection thereof.

4. An electrolyzer, as claimed in claim 1, having three saidelectrolysis compartments, in which an electrode located in the middleelectrolysis compartment is substantially twice as wide as thecorresponding electrodes located in the outer electrolysis compartments.

2. An electrolyzer, as claimed in claim 1, which includes partitionwalls between electrolysis compartments and collecting compartments andin which said cathode members comprise longitudinal members which aremade in the form of walls which form a lower portion of the partitionwalls.
 3. An electrolyzer, as claimed in claim 2, in which the thicknessof said longitudinal cathode members increases in the direction of thecurrent-conducting connection thereof.
 4. An electrolyzer, as claimed inclaim 1, having three said electrolysis compartments, in which anelectrode located in the middle electrolysis compartment issubstantially twice as wide as the corresponding electrodes located inthe outer electrolysis compartments.